Peripheral artery disease (PAD) is estimated to effect more than 200 million people worldwide. Peripheral artery disease (PAD) presents as either intermittent claudication (IC, pain with activity) or critical limb ischemia (CLI, constant rest pan with a high incidence of necrotic tissue loss). A common misconception is that CLI represents the nature progression of IC. In fact, patients with the same degree of stenosis can present with intermittent claudication, CLI, or can be symptom-free, suggesting that factors other than limb perfusion regulate CLI pathology. Current treatment approaches for PAD/CLI are focused on re-establishing blood flow to the ischemic tissue, implying that blood flow is the decisive factor tha determines whether or not the tissue survives. This project seeks to challenge this clinical paradigm. The discovery that inherent genetic and cell specific properties regulate the cellular response to ischemia/hypoxia, and thus determining the overall degree of tissue damage was initially a surprise because treatments have been aimed solely at recovering of blood flow. Mouse models of peripheral artery disease (PAD) in genetically protected (C57BL/6) and susceptible (BALB/c) inbred strains result in tissue necrosis and muscle myopathies that resemble the pathologies associated with human diagnoses of IC and CLI, respectively. In preliminary studies we discovered that rapid and severe loss of mitochondrial respiratory function is associated with increased muscle myopathy and tissue necrosis in BALB/c mice. Further, we provide evidence supporting that mitochondria are a viable therapeutic target for PAD. Finally, we have identified a genetic target, Cox6a2, which regulates the mitochondrial response to ischemia in skeletal muscle cells through alterations in its expression in response to ischemia. Based on these observations, we hypothesize that skeletal muscle mitochondria are critical regulator's of the response to ischemia, and therefore a primary determinant of myofibers regeneration, neovascularization, and tissue necrosis after limb ischemia. To investigate this hypothesis, the Specific Aims of this proposal are: 1) determine whether reduced skeletal muscle mitochondrial respiratory function increases the susceptibility to ischemic myopathy and limb tissue necrosis, 2) determine whether improved mitochondrial respiratory function in skeletal muscle protects against ischemic myopathy and limb tissue necrosis. Complimentary in vitro and in vivo experimental approaches will be used including physiological, pharmacological, and genetic gain- and loss-of-function models.